Ring-shaped insert molded article

ABSTRACT

A molded article  1  is configured such that an insert  2  is made of a steel plate and includes a cylindrical part  2 A and an annular part  2 B, a plastic  4  is annular in shape so as to be joined to the annular part  2 B, inner diameter D 1  of the plastic  4  is larger than inner diameter D 2  of the annular part  2 B so that no burrs at a gate mark E protrude to the inner diameter side of the molded article  1 , the injection molding is conducted with a disc gate arranged on an inner peripheral surface F of the plastic  4  at a position separated from a surface of the annular part  2 B, and the gate mark E resides on the inner peripheral surface F of the plastic  4  at a position separated from the surface of the annular part  2 B.

TECHNICAL FIELD

The present invention relates to a ring-shaped insert molded articlethat is manufactured by injection molding in a state where a thermosetadditive is applied to a joining surface of a ring-shaped insert to aplastic.

BACKGROUND

As ring-shaped insert molded articles manufactured by injection moldingin a state where a thermoset additive is applied to a joining surface ofa ring-shaped metallic part as an insert to a plastic and then theinsert and the plastic are placed in a metal mold, there have beensuggested axial (axially opposed-type) magnetic encoders (for example,refer to Patent Documents 1 and 2, and Patent Document 3, FIG. 2) andradial (radial opposed-type) magnetic encoders (for example, refer toPatent Document 3, FIG. 9 and Patent Document 4), which are used indevices for detecting the rotation speed of a rotating body.

Such injection molding of magnetic encoders is performed in many casessuch that a molten resin is injected into a metal mold from a disc gateplaced at the radially inner side of the insert molded article for theviewpoint of the orientation of magnetic substance powder in the moltenresin (refer to Patent Document 2, paragraphs [0017] to [0023], PatentDocument 3, paragraph [0034], and Patent Document 4, the description inthe prior art section).

CITATION LIST Patent Literatures

Patent Document 1: JP-A No. 2012-093125

Patent Document 2: JP-A No. 2006-133018

Patent Document 3: JP-A No. 2011-081008

Patent Document 4: JP-B No. H07-27833

SUMMARY OF THE INVENTION Technical Problems

In the magnetic encoders manufactured by disc gate-type insert moldingas described above, an additive layer intervenes between a supportmember as an insert and a plastic magnet (for example, refer to PatentDocument 1, paragraph [0026], Patent Document 2, paragraph [0035], andPatent Document 3, paragraph [0034]).

At manufacture of conventional magnetic encoders by disc gate-typeinsert molding, gate cutting is conducted in many cases at a boundarysurface between the support member and the plastic magnet, as can beseen from the gate placement in the axial magnetic encoder shown in FIG.5 of Patent Document 2 or the gate placement in the radial magneticencoder shown in FIG. 4 of Patent Document 4.

Thus, since foreign matter such as dust generated from the cut resin mayremain on the insert (for example, slinger 16 described in PatentDocument 2 or rotor yoke 1 described in Patent Document 4), it isnecessary to perform a post-process for removing the foreign matter. Inaddition, when the gate cutting is conducted on the boundary surface, ashearing load is applied to the boundary surface (joining surfacebetween the insert and the plastic magnet) that is low in strength,which may cause degradation of adhesive performance.

In addition, if a metal mold structure with the gate position aligned tothe inner peripheral surface of cylindrical part (annular part) of thering-shaped support member is used in the axial magnetic encoder, theforeign matter does not remain on the insert but burrs at the gate markprotrudes to the inner diameter side of the molded article. Thisrequires additional work for removing the burrs.

In view of the foregoing circumstances, an issue to be solved by thepresent invention is to provide a ring-shaped insert molded articlemanufactured by injection molding using a disc gate in a state where athermoset adhesive is applied to a joining surface of a ring-shapedinsert to a plastic and then the insert and the plastic are placed in ametal mold, wherein there is no need for the foregoing post-process oradditional work after gate cutting and the adhesive performance does notdeteriorate.

Solution to Problems

To solve the foregoing problems, a ring-shaped insert molded articleaccording to the present invention is a ring-shaped insert moldedarticle manufactured by injection molding in a state where a thermosetadhesive is applied to a joining surface of a ring-shaped insert to aplastic and then the insert and the plastic are placed in a metal mold,wherein the insert is made of a steel plate and includes a cylindricalpart and an annular part extended radially outward from one end edge ofthe cylindrical part, the plastic is annular in shape so as to be joinedto the annular part of the insert, the inner diameter of the plastic islarger than the inner diameter of the annular part so that no burrs at agate mark protrude to the inner diameter side of the molded article, theinjection molding is conducted with a disc gate arranged on an innerperipheral surface of the plastic at a position separated from a surfaceof the annular part, and in the gate-cut state, the gate mark resides onthe inner peripheral surface of the plastic at a position separated fromthe surface of the annular part so that no foreign matter resulting fromgate cutting sticks to the surface and no shearing load is applied bygate cutting to the joining surface to prevent degradation of adhesiveperformance.

According to this configuration, the inner diameter of the annularplastic is larger than the inner diameter of the annular part of thering-shaped insert so that no burrs at the gate mark protrude to theinner diameter side of the molded article, which thus eliminates theneed for additional work to remove the burrs.

In addition, in the gate-cut state, the gate mark resides on the innerperipheral surface of the plastic at a position separated from thesurface of the annular part so that no foreign matter resulting from thegate cutting sticks to the surface and no shearing load is applied bygate cutting to the joining surface to prevent deterioration in adhesiveperformance. This eliminates the need to perform the post-process forremoving the foreign matter because of absence of the foreign matter onthe surface and prevents degradation of adhesive performance caused bythe gate cutting.

It is preferred that the ring-shaped insert molded article is an axialmagnetic encoder in which the ring-shaped insert is a support member andthe plastic is a plastic magnet, the inner diameter of the plastic is0.6 mm or more larger than the inner diameter of the annular part, andthe gate mark resides at a position separated 0.1 mm or more from thesurface of the annular part.

According to this configuration, in the case where the ring-shapedinsert molded article is an axial magnetic encoder, it is ensured thatthe additional work and post-process are not needed after the gatecutting and degradation of adhesive performance caused by the gatecutting is prevented.

In addition, to solve the foregoing problems, a ring-shaped insertmolded article according to the present invention is a ring-shapedinsert molded article manufactured by injection molding in a state wherea thermoset adhesive is applied to a joining surface of a ring-shapedinsert to a plastic and then the insert and the plastic are placed in ametal mold, wherein the insert is made of a steel plate and includes acylindrical part and an annular part extended radially inward from oneend edge of the cylindrical part, the plastic is cylindrical in shape soas to be joined to an outer peripheral surface of the cylindrical partof the insert and has a curve part over the annular part, the injectionmolding is conducted with a disc gate arranged at a position separatedfrom a surface of the annular part on an inner peripheral surface of theplastic, and in the gate-cut state, the gate mark resides on the innerperipheral surface of the plastic at a position separated from thesurface of the annular part so that no foreign matter resulting fromgate cutting sticks to the surface and no shearing load is applied bygate cutting to the joining surface to prevent degradation of adhesiveperformance.

According to this configuration, the inner diameter of the curve part ofthe cylindrical plastic is sufficiently larger than the inner diameterof the annular part of the ring-shaped insert so that no burrs at thegate mark protrude to the inner diameter side of the molded article,which thus eliminates the need for additional work to remove the burrs.In addition, in the gate-cut state, the gate mark resides on the innerperipheral surface of the plastic at the position separated from thesurface of the annular part so that no foreign matter resulting from thegate cutting sticks to the surface and no shearing load is applied bygate cutting to the joining surface to prevent deterioration in adhesiveperformance. This eliminates the need to perform the post-process forremoving the foreign matter because of absence of the foreign matter onthe surface and prevents degradation of adhesive performance caused bythe gate cutting.

It is preferred that the ring-shaped insert molded article is a radialmagnetic encoder in which the ring-shaped insert is a support member andthe plastic is a plastic magnet, and the gate mark resides at a positionseparated 0.1 mm or more from the surface of the annular part.

According to this configuration, in the case where the ring-shapedinsert molded article is a radial magnetic encoder, it is ensured thatthe additional work and post-process are not needed after the gatecutting and degradation of adhesive performance caused by the gatecutting is prevented.

Advantageous Effects of Invention

According to each of the ring-shaped insert molded articles according tothe present invention as described above, the ring-shaped insert moldedarticle is manufactured by injection molding in a state where athermoset adhesive is applied to the joining surface of the ring-shapedinsert to the plastic and then the insert and the plastic are placed ina metal mold, which eliminates the need for the additional work toremove the burrs at the gate mark and the need to perform thepost-process for removing the foreign matter because of absence of theforeign matter on the surface resulting from the gate cutting, andprevents degradation of adhesive performance caused by the gate cutting.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a ring-shaped insertmolded article (axial magnetic encoder) according to a first embodimentof the present invention;

FIG. 2 is a longitudinal cross-sectional view of one example of aninjection mold for manufacturing the ring-shaped insert molded article;

FIG. 3 is an enlarged longitudinal cross-sectional view of majorcomponents of the injection mold;

FIG. 4 is an enlarged longitudinal cross-sectional view of majorcomponents, showing one example of a metal mold structure (insertcore-type): FIG. 4(a) shows a state in which, after mold clamping, amolten plastic is injected into the metal mold; FIG. 4(b) shows a statewhere the metal mold is cooled and then opened; and FIG. 4(c) shows astate where the molded article is removed from the metal mold, set on ajig, and then cut at a gate;

FIG. 5 is an enlarged longitudinal cross-sectional view of majorcomponents, showing one example of another metal mold structure (slidecore-type): FIG. 5(a) shows a state in which, after mold clamping, amolten plastic is injected into the metal mold; FIG. 5(b) shows a statewhere the metal mold is cooled and then opened; and FIG. 5(c) shows astate where the molded article is removed from the metal mold, set on ajig, and then cut at a gate;

FIG. 6 is a longitudinal cross-sectional view of a ring-shaped insertmolded article (radial magnetic encoder) according to a secondembodiment of the present invention;

FIG. 7 is an enlarged longitudinal cross-sectional view of majorcomponents, showing one example of a metal mold structure (insertcore-type): FIG. 7(a) shows a state in which, after mold clamping, amolten plastic is injected into the metal mold; FIG. 7(b) shows a statewhere the metal mold is cooled and then opened; and FIG. 7(c) shows astate where the molded article is removed from the metal mold, set on ajig, and then cut at a gate;

FIG. 8 is an enlarged longitudinal cross-sectional view of majorcomponents, showing one example of another metal mold structure (slidecore-type): FIG. 8(a) shows a state in which, after mold clamping, amolten plastic is injected into the metal mold; FIG. 8(b) shows a statewhere the metal mold is cooled and then opened; and FIG. 8(c) shows astate where the molded article is removed from the metal mold, set on ajig, and then cut at a gate.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will now be described below withreference to the drawings. The present invention is not limited to theembodiments shown in the drawings but includes all of embodimentsmeeting the requirements described in the patent claims.

First Embodiment

As shown in the longitudinal cross-sectional view of FIG. 1, aring-shaped insert molded article 1 according to a first embodiment ofthe present invention is manufactured by injection molding in a statewhere a thermoset adhesive is applied to a joining surface of aring-shaped insert 2 to a plastic 4 and then the ring-shaped insert 2and the plastic 4 are placed in a metal mold. An adhesive layer 6intervenes between the ring-shaped insert 2 and the plastic 4.

In addition, the ring-shaped insert molded article 1 is an axialmagnetic encoder A in which the ring-shaped insert 2 is a support memberand the plastic 4 is a plastic magnet.

The insert 2 is made of a steel plate and includes a cylindrical part 2Aand an annular part 2B extended radially outward from one end edge ofthe cylindrical part 2A. The ring-shaped insert 2 is formed by pressinga stainless-steel plate of 0.6 mm thick, for example.

The shape of the ring-shaped insert 2 is not limited to that shown inFIG. 1 as far as it includes at least the cylindrical part 2A and theannular part 2B.

The plastic 4 is annular in shape so as to be joined to the annular part2B of the ring-shaped insert 2. Inner diameter D1 of the plastic 4 islarger than an inner diameter D2 of the annular part 2B (inner diameterof the cylindrical part 2A) (D1>D2) so that no burrs at a gate mark Eprotrude to the inner diameter side of the molded article 1. Radialdistance G between an inner peripheral surface F of the plastic 4 and aninner peripheral surface of the ring-shaped insert 2 (inner peripheralsurface of the annular part 2B) is 0.3 mm or more (G≧0.3 mm). Thus, adifference between the inner diameter D1 of the plastic 4 and the innerdiameter D2 of the annular part 2B is 0.6 mm or more (D1−D2≧0.6 mm) andthickness T1 of the plastic 4 is 0.9 mm, for example.

In addition, the plastic 4 is formed by injection molding such that adisc gate described later is arranged on an inner peripheral surface Fat a position separated from the surface of the annular part 2B. In thegate-cut state, the gate mark E resides on the inner peripheral surfaceF of the plastic 4 at a position separated from the surface of theannular par 2B, and a distance L1 from the surface of the annular part2B to the gate mark E is 0.1 mm or more (L1≧0.1 mm), so that no foreignmatter resulting from gate cutting sticks to the surface and no shearingload is applied by gate cutting to the joining surface between thering-shaped insert 2 and the plastic 4 to prevent degradation ofadhesive performance as described later.

The plastic (plastic magnet) 4 is formed by a magnetic materialcontaining magnetic substance powder, a binder, and an additive. Themagnetic substance powder may be preferably magnetic powder based onferrite such as strontium ferrite or barium ferrite, or rare-earthmagnetic powder based on neodymium or samarium. The binder may bepreferably a thermoplastic resin material such as polyamides (PA6, PA12,PA612, and the like) or polyphenylene sulfide (PPS). The additive may bepreferably an organic additive such as carbon fiber, or an inorganicadditive such as glass beads, glass fiber, talc, mica, silicon nitride(ceramic), or crystalline (non-crystalline) silica.

Next, an example of injection molding for manufacturing the ring-shapedinsert molded article 1 according to the first embodiment of the presentinvention will be described.

As shown in the longitudinal cross-sectional view of FIG. 2 and theenlarged longitudinal cross-sectional view of major components of FIG.3, an injection mold 8 is intended to mold the ring-shaped insert moldedarticle 1 (axial magnetic encoder A) and is attached to an injectionmolding machine by fixing a fixed attachment plate 9 to a fixed platenwith a bolt and fixing a movable attachment plate 10 to a movable discwith a bolt.

In a state where a thermoset adhesive is applied to the joining surfaceof the ring-shaped insert 2 to the plastic 4 and then the ring-shapedinsert 2 and the plastic 4 are placed in a fixed mold plate 11 and amovable mold plate 12 and then the mold plates are clamped, when amolten plastic P is poured into a sprue 13, the molten plastic P flowsthrough a disc gate 15 via a runner 14 and is filled into a cavity Cbetween the fixed mold plate 11 and the movable mold plate 12 (referalso to the enlarged longitudinal cross-sectional view of majorcomponents of FIG. 4(a)).

The direction of extension of the sprue 13 (in which the molten plasticP is poured) is horizontal.

After the molten plastic P is cooled and hardened, as shown in theenlarged longitudinal cross-sectional view of major components of FIG.4(b), the movable mold plate 12 is opened from a parting line PL and apre-gate cutting molded article and an insert core 18A are projected andejected by ejectors 16 and 17 (refer to FIGS. 2 and 3), therebyobtaining the pre-gate cutting molded article and the insert core 18A.

Next, as shown in the enlarged longitudinal cross-sectional view ofmajor components of FIG. 4(c), while the pre-gate cutting molded articleand the insert core 18A removed from the metal mold are set on a jig20A, the molded article is pressurized by a pusher 21A to cut the gate.Thus, the gate mark E remains on the ring-shaped insert molded article 1(axial magnetic encoder A).

At the gate cutting as shown in FIG. 4(c), the insert core 18A is placedalong the gate cutting part of the plastic such that the insert core 18Aserves as a cutting blade to cut the gate by shearing action. Thisreduces load on the product at the time of gate cutting.

Next, an example of a metal mold structure different from the insertcore type as shown in FIG. 4 will be described.

The enlarged longitudinal cross-sectional view of major components ofFIG. 5 shows a slide core-type metal mold structure.

After the molten plastic P is filled into the cavity C and then iscooled and hardened as shown in FIG. 5(a), a slide core 19A is slidradially inward and separated from the molded article as shown in FIG.5(b). In this state, the movable mold plate 12 is opened from theparting line PL and a pre-gate cutting molded article is projected andejected by the ejector 16 (refer to FIG. 2). Thus, the pre-gate cuttingmolded article is obtained.

Next, as shown in FIG. 5(c), while the pre-gate cutting molded articleremoved from the metal mold is set on the jig 20A, the molded article ispressurized by the pusher 21A to cut the gate. The gate mark E remainson the ring-shaped insert molded article 1 (axial magnetic encoder A).

According to the configuration of the ring-shaped insert molded article1 (axial magnetic encoder A) in the first embodiment, the inner diameterD1 of the annular plastic 4 is larger than the inner diameter D2 of theannular part 2B of the ring-shaped insert 2 so that no burrs at the gatemark E protrude to the inner diameter side of the molded article 1,which thus eliminates the need for additional work to remove the burrs.

In addition, in the gate-cut state, the gate mark E resides on the innerperipheral surface F of the plastic 4 at a position separated from thesurface of the annular part 2B so that no foreign matter resulting fromthe gate cutting sticks to the surface and no shearing load is appliedby gate cutting to the joining surface between the ring-shaped insert 2and the plastic 4 to prevent deterioration in adhesive performance. Thiseliminates the need to perform a post-process for removing the foreignmatter because of absence of the foreign matter on the surface andprevents degradation of adhesive performance caused by the gate cutting.

In addition, in the case where the ring-shaped insert molded article 1is an axial magnetic encoder A in which the ring-shaped insert 2 is asupport member, the plastic 4 is a plastic magnet, the inner diameter D1of the plastic 4 is 0.6 mm or more larger than the inner diameter D2 ofthe annular part 2B, and the gate mark E resides at a position separated0.1 mm or more from the surface of the annular part 2B, and further inthe case where the ring-shaped insert molded article 1 is an axialmagnetic encoder A, it is ensured that the additional work andpost-process are not needed after the gate cutting and degradation ofadhesive performance caused by the gate cutting is prevented.

Second Embodiment

As shown in the longitudinal cross-sectional view of FIG. 6, thering-shaped insert molded article 1 according to a second embodiment ofthe present invention is manufactured by injection molding in a statewhere a thermoset adhesive is applied to a joining surface of aring-shaped insert 3 to a plastic 5 and then the ring-shaped insert 3and the plastic 5 are placed in a metal mold, and the adhesive layer 6intervenes between the ring-shaped insert 3 and the plastic 5.

In addition, the ring-shaped insert molded article 1 is a radialmagnetic encoder B in which the ring-shaped insert 3 is a support memberand the plastic 5 is a plastic magnet.

The ring-shaped insert 3 is made of a steel plate and includes acylindrical part 3A and an annular part 3B extended radially inward fromone end edge of the cylindrical part 3A. The ring-shaped insert 3 isformed by pressing a stainless-steel plate of 0.6 mm thick, for example.

The shape of the ring-shaped insert 3 is not limited to that shown inFIG. 6 as far as it includes at least the cylindrical part 3A and theannular part 3B.

The material for the plastic (plastic magnet) 5 is the same as that inthe first embodiment. The plastic 5 is cylindrical in shape so as to bejoined to the outer peripheral surface of the cylindrical part 3A of thering-shaped insert 3, and has a curve part 7 over the annular part 3B.Thickness T2 of the plastic 5 is 0.9 mm, for example.

In addition, the plastic 5 is injection-molded such that a disc gate isarranged on the inner peripheral surface F at a position separated fromthe surface of the annular part 3B. In the gate-cut state, the gate markE resides on the inner peripheral surface F of the plastic 5 at aposition separated from the surface of the annular part 3B, and adistance L2 from the surface of the annular part 3B to the gate mark Eis 0.1 mm or more (L2≧0.1 mm), so that no foreign matter resulting fromgate cutting sticks to the surface and no shearing load is applied bygate cutting to the joining surface between the ring-shaped insert 3 andthe plastic 5 to prevent degradation of adhesive performance asdescribed later.

Next, an example of injection molding for manufacturing the ring-shapedinsert molded article 1 according to the second embodiment of thepresent invention will be described.

The ring-shaped insert molded article 1 (radial magnetic encoder B) canbe manufactured using the same metal mold as the injection mold 8 shownin FIG. 2. After the molten plastic P is filled into the cavity C andthen is cooled and hardened as shown in the enlarged longitudinalcross-sectional view of major components of FIG. 7(a), the movable moldplate 12 is opened from the parting line PL and a pre-gate cuttingmolded article and an insert core 18B are projected and ejected by theejectors 16 and 17 (refer to FIG. 2), thereby obtaining the pre-gatecutting molded article and the insert core 18B as shown in the enlargedlongitudinal cross-sectional view of major components of FIG. 7(b).

Next, as shown in the enlarged longitudinal cross-sectional view ofmajor components of FIG. 7(c), while the pre-gate cutting molded articleand the insert core 18B removed from the metal mold are set on a jig20B, the molded article is pressurized by a pusher 21B to cut the gate.The gate mark E remains on the ring-shaped insert molded article 1(radial magnetic encoder B).

At the gate cutting as shown in FIG. 7(c), the insert core 18B is placedalong the gate cutting part of the plastic such that the insert core 18Bserves as a cutting blade to cut the gate by shearing action. Thisreduces load on the product at the time of gate cutting.

Next, an example of a metal mold structure different from the insertcore type shown in FIG. 7 will be described.

The enlarged longitudinal cross-sectional view of major components ofFIG. 8 shows a slide core-type metal mold structure.

After the molten plastic P is filled into the cavity C and then iscooled and hardened as shown in FIG. 8(a), a slide core 19B is slidradially inward and separated from the molded article as shown in FIG.8(b). In this state, the movable mold plate 12 is opened from theparting line PL and a pre-gate cutting molded article is projected andejected by the ejector 16 (refer to FIG. 2). Thus, the pre-gate cuttingmolded article is obtained.

Next, as shown in FIG. 8(c), while the pre-gate cutting molded articleremoved from the metal mold is set on the jig 20B, the molded article ispressurized by the pusher 21B to cut the gate. The gate mark E remainson the ring-shaped insert molded article 1 (radial magnetic encoder B).

According to the configuration of the ring-shaped insert molded article1 (radial magnetic encoder B) in the second embodiment, the innerdiameter of the curve part 7 of the cylindrical plastic 5 issufficiently larger than the inner diameter of the annular part 3B ofthe ring-shaped insert 3, and thus no burrs at the gate mark E protrudeto the inner diameter side of the molded article 1, which thuseliminates the need for additional work to remove the burrs.

In addition, in the gate-cut state, the gate mark E resides on the innerperipheral surface F of the plastic 5 at a position separated from thesurface of the annular part 3B so that no foreign matter resulting fromthe gate cutting sticks to the surface and no shearing load is appliedby gate cutting to the joining surface between the ring-shaped insert 3and the plastic 5 to prevent deterioration in adhesive performance. Thiseliminates the need to perform a post-process for removing the foreignmatter because of absence of the foreign matter on the surface andprevents degradation of adhesive performance caused by the gate cutting.

In addition, in the case where the ring-shaped insert molded article 1is a radial magnetic encoder B in which the ring-shaped insert 3 is asupport member, the plastic 5 is a plastic magnet, and the gate mark Eresides at a position separated 0.1 mm or more from the surface of theannular part 3B, and further in the case where the ring-shaped insertmolded article 1 is a radial magnetic encoder B, it is ensured that theadditional work and post-process are not needed after the gate cuttingand degradation of adhesive performance caused by the gate cutting isprevented.

In the foregoing descriptions, the ring-shaped insert molded article isan axial magnetic encoder or a radial magnetic encoder. However, thering-shaped insert molded article of the present invention is notlimited to them but can be manufactured in any manner by injectionmolding in the state where a thermoset adhesive is applied to thejoining surface of the ring-shaped insert to the plastic and then theinsert and the plastic are placed in the metal mold, such as an insertmolded article with replacement of a ring-shaped metal.

In addition, the ring-shaped molded article of the present invention isconfigured such that, in the gate-cut state, the gate mark resides onthe inner peripheral surface of the plastic at a position separated fromthe surface of the annular part so that no foreign matter resulting fromthe gate cutting sticks to the surface and no shearing load is appliedby gate cutting to the joining surface between the insert and theplastic to prevent deterioration in adhesive performance. Thiseliminates the need to perform the post-process for removing the foreignmatter because of absence of the foreign matter on the surface andprevents degradation of adhesive performance caused by the gate cutting.Besides, no burrs at the gate mark protrude to the inner diameter sideof the molded article, which thus eliminates the need for additionalwork to remove the burrs. However, the process for removing the burrsmay be performed on the ring-shaped insert molded article, depending onthe specifications for the ring-shaped insert molded article.

REFERENCE SIGNS LIST

-   A Axial magnetic encoder-   B Radial magnetic encoder-   C Cavity-   D1 Inner diameter of plastic-   D2 Inner diameter of annular part-   E Gate mark-   F Inner peripheral surface of plastic-   G Radial distance between inner peripheral surface of plastic and    inner peripheral surface of insert-   L1, L2 Distance from surface of annular part to gate mark-   P Molten plastic-   PL Parting line-   T1, T2 Thickness-   1 Ring-shaped insert molded article-   2, 3 Ring-shaped insert-   2A, 3A Cylindrical part-   2B, 3B Annular part-   4, 5 Plastic-   6 Adhesive layer-   7 Curve part-   8 Injection mold-   9 Fixed attachment plate-   10 Movable attachment plate-   11 Fixed mold plate-   12 Movable mold plate-   13 Sprue-   14 Runner-   15 Disc gate-   16, 17 Ejector-   18A, 18B Insert core-   19A, 19B Slide core-   20A, 20B Jig-   21A, 21B Pusher

1. (canceled)
 2. (canceled)
 3. A ring-shaped insert molded articlemanufactured by injection molding in a state where a thermoset adhesiveis applied to a joining surface of a ring-shaped insert to a plastic andthen the insert and the plastic are placed in a metal mold, wherein theinsert is made of a steel plate and includes a cylindrical part and anannular part extended radially inward from one end edge of thecylindrical part, the plastic is cylindrical in shape so as to be joinedto an outer peripheral surface of the cylindrical part of the insert andhas a curve part over the annular part, the injection molding isconducted with a disc gate arranged on an inner peripheral surface ofthe plastic at a position separated from a surface of the annular part,and in the gate-cut state, a gate mark resides on the inner peripheralsurface of the plastic at a position separated from the surface of theannular part so that no foreign matter resulting from gate cuttingsticks to the surface and no shearing load is applied by gate cutting tothe joining surface to prevent degradation of adhesive performance. 4.The ring-shaped insert molded article according to claim 3, wherein thering-shaped insert molded article is a radial magnetic encoder in whichthe ring-shaped insert is a support member and the plastic is a plasticmagnet, and the gate mark resides at a position separated 0.1 mm or morefrom the surface of the annular part.